#!/bin/sh

# whatyear weekday month day 
#    given a month, day, and day of week figure out the most recent year it occurred

temp=".$0.tmp"

figureDOW()
{
  # give this day of month, month and year and it'll return day of week, 1-7

  day=$1;  caldate="$2 $3"

  expr="[^0-9]${day}[^0-9]"

  cal $caldate | sed 's/^/ /;s/$/ /' > $temp

  NRval=$(cat $temp | awk "/$expr/ { print NR }")
  NFval=$(cat $temp | awk "/$expr/ { print NF }")

  if [ $NRval -eq 3 ] ; then
    DOW="$(( $day + ( 7 - $NFval ) ))"
  else
    DOW=$(cat $temp | awk "/$expr/ { for (i=1;i<=NF;i++) { if (\$i~/${day}/) { print i }}}")
  fi
  /bin/rm -f $temp
}

if [ $# -ne 3 ] ; then
  echo "Usage: $(basename $0) weekday month day" 
  echo "  (example: $(basename $0) wed aug 3  )"
  exit 1
fi

weekday=$(echo $1 | tr '[[:upper:]]' '[[:lower:]]' | cut -c1-3)
  month=$(echo $2 | tr '[[:upper:]]' '[[:lower:]]' | cut -c1-3)
    day=$3

# convert weekday = DOW numeric value

desiredDOW=$(echo $weekday | sed 's/sun/1/;s/mon/2/;s/tue/3/;s/wed/4/;s/thu/5/;s/fri/6/;s/sat/7/')

# get the current month, day and year

# echo $(date "+thismonth=%m; thisday=%d; thisyear=%Y")
eval $(date "+thismonth=%m; thisday=%d; thisyear=%Y")

# now convert month name into abbrev, then figure numerical equivalent

monthnum=$(echo $month | sed 's/jan/1/;s/feb/2/;s/mar/3/;s/apr/4/;s/may/5/;s/jun/6/' | \
   sed 's/jul/7/;s/aug/8/;s/sep/9/;s/oct/10/;s/nov/11/;s/dec/12/')

# now, is the mon/day possibly this year?  Only if it's in the past...

if [ $monthnum -gt $thismonth ] ; then
  # month is in the future, can't be this year
  mostrecent=$(( $thisyear - 1 ))
elif [ $monthnum -eq $thismonth -a $day -gt $thisday ] ; then
  # right month, but seeking a date in the future
  mostrecent=$(( $thisyear - 1 ))
else
  mostrecent=$thisyear
fi

# echo Looking for $weekday, $day, $month \($monthnum\) starting in $mostrecent 

# now we need to loop through years, decrementing, until a match

year=$mostrecent
DOW=-1			# start with a dead value

while [ $DOW -ne $desiredDOW ] 
do
  figureDOW $day $monthnum $year
# echo "> $day $month occurred on a $DOW in $year"
  year=$(( $year - 1 ))
done

echo "Got it! $day $month occurred on a $weekday most recently in ${year}:"
cal $month $year


exit 0